This invention relates to the oxidation of sulphide minerals, including the recovery of gold from sulphide minerals, by means of biological oxidation.
Biological oxidation of sulphide ores, especially pyritic gold ores, has been known for some time and there are many references in the literature to ore processing in this way.
The specification of South African patent No. 90/2244 describes such a process which makes use of bacteria which are capable of oxidising the various sulphide minerals in the ore to release gold particles for subsequent recovery by known techniques.
The biological process has a number of advantages relating to the commercial recovery of a desired element from a sulphide mineral. It does however suffer from at least two disadvantages. Firstly the process is relatively slow and takes several days, of the order of from four to six days, to go to completion.
Secondly the process has been found to function most efficiently when a relatively dilute water slurry of the ore is passed through a series of agitated tanks in succession. As the slurry is dilute, typically with from 10 to 20% solids content, the tanks which are required for the slurry are large.
The process is usually conducted in a series of tanks. The first tank in the series is the most important because it is here that oxidation is initiated and where bacterial growth is maintained. The subsequent tanks in series are used to complete the oxidation of the sulphide minerals. Usually at least half of the work of oxidation is completed in the first tank. It would be advantageous if the products of oxidation could be separated from the minerals which are not yet oxidised. In this way the size of second and subsequent tanks in series could be smaller in size.
The invention lends itself to the recovery of precious metals i.e. gold, silver and the platinum group metals, and also to the recovery of base metals e.g. cobalt, nickel, copper etc.